1. Field of the Invention
This invention relates generally to an insulating glass unit and, in particular, to a moisture impervious sealant system for an insulating glass unit and a method of making same.
2. Description of the Currently Available Technology
It is well recognized that insulating glass (IG) units reduce the heat transfer between the outside and inside of a building or other structure. Examples of IG units are disclosed in U.S. Pat. Nos. 4,193,236; 4,464,874; 5,088,258; and 5,106,663 and European reference EP 65510, the teachings of which are herein incorporated by reference. A sealant system or edge seal structure of the prior art is shown in FIG. 1. The IG unit 10 of FIG. 1 includes two spaced apart glass sheets 12 and 13 adhesively bonded to a rigid spacer frame 14 by a sealant system 15 to provide a chamber 16 between the two glass sheets 12 and 13. The chamber 16 can be filled with a selected atmosphere, such as argon or krypton gas, to enhance the performance characteristics of the IG unit 10. The sealant system 15 bonding the glass sheets 12 and 13 to the spacer frame 14 are expected to provide structural strength to maintain the unity of the IG unit 10 and prevent gas leaking out of the chamber 16 or the atmosphere from outside the IG unit 10 from moving into the chamber 16. The sealant system 15 includes a layer 17 of moisture resistant sealant at the upper section of the spacer 14 to prevent the ingress and egress of gas into and out of the chamber 16 and a layer 18 of a structural type sealant, such as silicone to secure the sheets to the spacer. A moisture resistant sealant usually used in the art is polyisobutylene (PIB).
In addition to adhering the two glass sheets 12 and 13 to the spacer frame 14 and forming a moisture impervious barrier, the sealant system 15 should accommodate the natural tendency for the edges of the glass sheets 12 and 13 to rotate or flex due to changes in atmospheric pressure in the chamber 16 as a result of temperature, wind load and altitude changes, such as when an IG unit is manufactured at one altitude and installed at a different altitude. The spacer and selected sealant system should maintain the structural integrity of the IG unit as well as the sealing properties of the edge seal structure even during such changes.
As will be appreciated, box spacer frames 14, such as shown in FIG. 1, are not well suited for allowing such flexibility. For example and with reference to FIG. 2, as the distance between the sheets 12 and 13 increases because of pressure differences inside and outside of the chamber 16, the sealant system 15, in particular the layer 17 of the moisture resistant sealant, stretches and thins under stress, which decreases its ability to prevent atmospheric air from moving into and/or gas escape from the chamber 16. With rigid, box spacer frames, the structural sealant system 15 tends to become over stressed with time and fails prematurely. Additionally, the rigid spacer frame itself may become over-stressed and may collapse or deform or the glass sheets may become over-stressed at the edges and crack. Further, if the chamber between the glass sheets is filled with gas such as argon, krypton or other such insulating gas, the deformation of the sealants 17 and 18 and/or spacer frame 14 often results in accelerated loss of those gases from the chamber into the surrounding atmosphere.
An alternative to the prior art arrangement shown in FIG. 1 is to use a more flexible spacer frame, e.g. of the type disclosed in U.S. Pat. Nos. 5,655,282; 5,675,944; 5,177,916; 5,255,481; 5,351,451; 5,501,013; and 5,761,946, the teachings of which are herein incorporated by reference. While such flexible spacer frames help alleviate some of the problems encountered with rigid spacer frames, the use of flexible spacer frames in and of themselves may not completely eliminate the edge breakage and vapor and/or gas transmission problems associated with known edge seal and/or IG unit construction.
Therefore, it would be advantageous to provide an IG unit having a sealant system which reduces or eliminates the problems associated with known spacer frame and adhesive construction and a method of fabricating such an IG unit.